A sliding clutch of this type is described in U.S. Pat. No. 4,891,090 to Lorinez et al. (corresponding to EP 0 362 697 A1). This known sliding clutch is disposed between a rotary drive member for a supply reel with the sliding clutch comprising two bearing members arranged concentrically within one another, one of these bearing members having the form of a round ring and the other bearing member being formed by a hollow cylindrical reel body. The round ring is made up of a plurality of annular segments formed by radial and axial slots which extend axially in one piece from a toothed disc while engaging concentrically in the hollow cylindrical reel body. It is guaranteed that slidable torsional slaving can be achieved by the ring segments pressing radially against the inner shell surface of the hollow cylindrical reel body with a certain amount of tensional force at its free end portions as a result of a prefabricated oversized portion.
In this known sliding clutch, it is difficult to predetermine the size of the torque at which the transmission force is to be limited. This is caused by the level having to be predetermined during manufacture of the annular segments as they have to be produced with a radially oversized section so that they abut such that they are elastically pushed together with a radial bias at the inner shell surface of the reel body in the mounted position. In doing so, it has to be taken into consideration that even slight angular deviations of the annular segments can lead to a considerable radial change in position of their effective friction surfaces and a predetermined torque restriction can therefore only be implemented within a large tolerance range. In addition, in the known design, one has to expect alterations in tension caused by relatively high stress existing at the connection point between the annular segments and the toothed disc because of the desired small design which, for one thing, is inclined to decrease stress because of the material becoming fatigued and, for another thing, leans towards an unintentional increase or decrease in frictional tension as a result of changes in shape caused by differences in temperature. For reasons connected with handling and the defect-free transportation of the backing tape and the film, it is however desired to achieve as uniform a tension of the frictional surfaces on one another and as uniform a torque slaving as possible.
U.S. Pat. No. 6,145,770 to Manusch et al. (corresponding to EP 0 883 564 B1) describes a sliding clutch for torque-limiting force transmission between a reel core and a reel for winding up or unwinding a tape which has two rotating parts arranged concentrically within one another, one of which has the shape of an oval ring with an annular wall which is radially elastically deformable towards the rotational axis and where the torsional force is transmitted by frictional slaving between the oval annular wall and the other bearing member provided in the form of a polygon. In this known structure, the ring is severely deformed and a concentric bearing of the rotating parts is not guaranteed either.
A need exists for improving the frictional slaving of a sliding clutch of the type described above while guaranteeing a simple concentric mounting. A need also exists for the improved torque-limiting transmission of force and to make it easier to predetermine the force more precisely. Furthermore, the sliding clutch should have a long lifetime with the maximum transferable torque of the force transmission not substantially changing over a longer period of time or remaining constant.